Two or more units travelling in formation and intended for laying concrete or asphalt material and producing a continuous surface layer having a desired surface profile along a predetermined path are designated as a paving train. Such paving trains are used in particular in the construction of traffic areas, such as in the production and repair of roads and squares. The units used in the paving train are, for example, at least one spreader and at least one finisher—such as a slipform paver or an asphalt paver. Likewise known is the use of two or more finishers in one paving train. The finisher is generally followed by a spray vehicle which sprays chemicals onto the surface which prevent excessively fast drying of the material.
In the paving process, the material to be laid is usually delivered by means of a loader unit, such as a truck or a mixer, and is unloaded along the predetermined path. The spreader is equipped with a distributing member, such as a screw, for distributing material and carries out a transverse distribution and in general also an initial smoothing of the material. The coarse smoothing is effected by means of a drawing device of the spreader in such a way that approximately the desired height of the surface layer is achieved.
Trailing behind the spreader at a predeterminable distance, the finisher then draws the material by means of its characteristic beam, which, for example, may be a screeding beam or may have a profile, so that the desired height of the surface layer is achieved with generic accuracy—in the millimetre range.
For guiding the paving train along the predetermined path and optionally also for vertical positioning of the working parts of the units—such as the paving beam, the drawing device and the distributing member—it is usual to stretch a reference line—e.g. a wire cable—along which guidance takes place. This takes place by means of distance sensors which are linked to the automatic control system of the machines. Units trailing behind the rearmost finisher—such as the spray vehicle—generally do not use the reference line for longitudinal scanning, but the laid surface layer.
As an alternative to reference line scanning, the finisher is controlled via a position or attitude determination system. For example, the position of the finisher is determined via a position element arranged thereon—or a plurality of position elements. This is, for example, a GPS receiver which receives position data from satellites, or a reflector whose position is measured by means of a total station. The position thus determined is compared—for example in a ground model—with a theoretical position, control instructions being derived from the comparison. The control instructions relate to the direction control/steering control of the finisher unit, to the vertical positioning—working height—of the beam and optionally to the horizontal one-dimensional or two-dimensional orientation of the finisher unit and of the beam. The determination of the working height can be effected according to the mounting of the position element from the position thereof or via an additional reference determination.
Such methods and devices for controlling a finisher and/or the working height of the paving beam thereof are described, for example, in EP 1 079 029 A2, the unpublished US patent application with the application Ser. No. 11/071,942 or the unpublished European patent application with the application number 04029963.8.
These position or attitude determination methods for control have been developed for high accuracies with regard to the surface layer to be produced and accordingly require complex components and data processing methods Only the finishers operating with the highest accuracy are therefore controlled in this way. This gives rise to the situation that the finisher is controlled in a highly precise manner via a position or attitude determination system but the remaining units of the paving train still require the less complex but extremely labour-intensive reference line method for control. The reference line method requires measurement and laying out the area to be processed before the beginning of the paving work. This complicated preparation is necessary in spite of alternative control of the finisher—for example only for one spreader.